This invention relates to the utilization of electromagnetic (EM) radiation for treating selected dermatologic problems, and more particularly to a system which utilizes temperature detection at a waveguide though which radiation is being applied to the patient""s skin to perform various control functions and to a head usable in such system or elsewhere, which head includes efficient reflectors for back-scattered radiation and/or for otherwise enhancing irradiation of a target volume containing the dermatologic problem.
Lasers, lamps and other sources of electromagnetic radiation are being increasingly utilized to treat various dermatological conditions, and in particular for the removal of unwanted hair, spider veins, leg veins, other veins or blood vessels which are visible through the patient""s skin, lesions, port-wine stains, tattoos and the like. One problem with such treatments is that the only way to get the radiation to a target volume in the dermis where treatment is desired is to transmit the radiation to such volume through the overlying epidermis. Further, since many of the treatments involve absorption of energy by melanin in the dermal volume being treated, for example in a hair follicle, and there is also melanin in the epidermis, particularly in the portion thereof at the dermal/epidermal (DE) junction, the EM radiation used for treatment is generally also absorbed to varying degrees in the epidermis. Further, the deeper in the dermis the treatment is desired and/or the larger the element being treated, the more energy must be used, this generally involving use of a more powerful laser or other radiation source with higher fluence and/or operating such source for longer time durations. However, as the energy applied through the epidermis increases, the potential for damage to the epidermis as a result of energy absorption therein also increases.
Therefore, one limitation on the energies which can be used for various dermatological treatments in the dermis, and in particular on the depths in the dermis at which treatment can be performed, and on the size of the elements which can be treated, is that the energy applied cannot be so high as to cause appreciable damage to the epidermis. Various ways around this problem have been proposed in the prior art, most of which involve some cooling of the epidermis prior to and/or during treatment to limit or prevent thermal damage thereto. Examples of such procedures include applying cryogenic or other cooling sprays to the skin, applying a cooling gel to the skin, applying radiation through a cold-pack in contact with the skin or through an applicator which is cooled by flowing water, flowing air, or the like. However, these prior art systems have not been wholly satisfactory. One reason for this is that, since most of the absorption is in the melanin located in the lower portions of the epidermis, it is desirable to have cooling through the entire epidermal layer, which is typically about 0.1 mm thick. However, it is not desirable that the cooling extend significantly below the DE junction into the dermal layer since cooling in the dermal layer can potentially inhibit the desired thermal damage to follicles, blood vessels or the like in this region. Further, there are significant variations in radiation absorption by a patients skin, not only among different individuals, people having darker skin absorbing more radiation and being more prone to epidermal damage than people with lighter skin, but even for different areas on the body of a single individual. Therefore, cooling which is not customized to the treatment area generally results in the cooling not being to the proper depth, a problem which can interfere with treatment and/or permit thermal damage to the epidermis.
It would therefore be desirable if the temperature at a selected depth in the skin, for example the DE junction, could be measured, and this temperature utilized to control skin temperature, for example through the epidermis, by some combination of controlling the laser energy applied to skin and/or controlling cooling applied to the skin. However, while infrared sensors have for example been utilized in the past to detect temperature at the surface of the skin, such detection does not provide an accurate indication of temperature even at the skin surface, these readings varying with such factors as skin layer thickness, skin roughness and skin color in addition to temperature. Infrared sensors also provide virtually no information as to skin temperature at a depth below the surface. Therefore, such detection has heretofore been used only for gross controls, for example to turn off the laser if an emergency temperature threshold is exceeded or the like, but not to fine tune energy application and/or cooling so as to maintain a desired temperature at a selected depth, for example at the DE junction, thereby facilitating a desired treatment without epidermal damage.
A need therefore exists for an improved technique which permits more accurate determinations of skin temperature at various depths, including at the DE junction, so as to permit more accurate and more automatic control of EM radiation treatments for various dermatological conditions. In particular, because of variations in skin pigmentation, differences in epidermal depth, and other dermatological differences among patients, laser dermatology procedures are now performed almost exclusively by physicians or other highly trained individuals, and such individuals must exercise great care to assure that epidermal damage does not occur, while still achieving the desired therapeutic effect. More accurate measurement of temperature at desired depths would make treatments by such skilled personnel easier to perform and would permit such procedures to be safely performed by less highly trained, and therefore less expensive, personnel. Such skin temperature measurements could also be utilized to determine skin type/pigmentation for the patient and/or for the part of a patient""s body being treated and/or for other purposes.
Where cooling of the epidermis is achieved by placing a cooled applicator or other cooled body in contact with the patient""s skin, the contact must be made with sufficient pressure to assure good thermal contact between the cooled body and the skin. However, differences in skin thickness and elasticity, differences in bone backing and other factors affect the pressure required to achieve good thermal contact for different patients and for different areas on the body for the same patient. This is another reason why highly trained and skilled individuals are required for performing the treatments and contributes to the high cost of the treatment. It would therefore be preferable if an automatic technique could be provided for detecting, and thus assuring, good thermal contact between a cooling element and the patient""s skin. Such a technique or mechanism, by assuring good thermal contact with the skin before the radiation source is fired, could solve two critical safety problems for radiation dermatology. First, it assures adequate cooling of the epidermis before heating thereof through energy absorption; and second, it assures that the radiation will not be accidentally applied to the eyes or other unwanted place.
Related but opposite problems arise in performing certain skin resurfacing/wrinkle removal procedures where the objective is to heat and destroy only the most surface layer of the skin, for example the epidermis, with minimal damage to underlying layers. This requires tight control of factors such as laser energy, pulse duration and repetition rate. However, variations in patient""s skin make such tight control difficult even for highly trained and skilled personnel. Similar problems also arise in other dermatological procedures involving lasers or other radiation sources.
Another related problem in using an EM radiation source for dermatological treatment is that the skin reflects back a significant portion of the radiation applied thereto. Since this reflected energy does not reach the treatment site, a higher energy radiation source is required to achieve the desired dermatological treatment than would be the case if a larger percentage of the applied radiation reached the treatment site. It has previously been suggested that one solution to this problem is to provide a retro-reflector which collects and returns such back-scattered radiation to the patient""s skin. However, existing retro-reflector devices have not optimized the collection and return of such back-scattered radiation and improved techniques for the more efficient reutilization of back-scattered radiation is therefore desirable. One particular problem with prior art retroreflectors is that they reflect all back-scattered radiation at substantially the same angle the radiation was received; however, radiation at an angle more parallel than perpendicular to the skin surface generally does not reach the treatment area and therefore only heats the surface of the skin, contributing to thermal damage of the skin, without having any beneficial/therapeutic effect. A retroreflection technique which does not contribute to or increase this xe2x80x9cparallelxe2x80x9d radiation would therefore be desirable.
Two other factors can contribute to the efficiency of dermatologic treatments. The first factor is xe2x80x9cspot sizexe2x80x9d or in other words the optical aperture of the applied radiation. Spot size is typically limited by the optics of the handpiece utilized and by the desired fluence as a function of the available energy source. However, a larger spot size permits treatment of large body areas such as back or legs to be accomplished much more quickly, something which enhances both patient satisfaction and practitioner profitability. A technique for facilitating larger spot sizes is thus desirable.
Secondly, anything which reduces the distance from the irradiation source to the target area reduces the amount of energy required to achieve a desired therapeutic effect and anything which permits more of the applied energy to reach the target area has a similar effect. Techniques which facilitate the achievements of these objectives are therefore also desirable.
In accordance with the above this invention provides both a system for treating a selected dermatologic problem and a head for use in such system. The head, for preferred embodiments includes an optical waveguide or other light path for directing EM radiation of a wavelength appropriate for treating the selected patient dermatologic problem to a first end of the waveguide, the waveguide also having a skin-contacting second end which is opposite the first end; and a sensor at the second end of the waveguide, or otherwise closely adjacent a skin-contacting surface of the head, which senses the temperature thereat. For preferred embodiments, the head also includes a mechanism for removing heat from the waveguide. In order to achieve commercially useful sensitivity, it is preferable that the sensor be located no more than a few millimeters from the skin-contacting surface of the head, for example, the second end of the waveguide, the end contacting the patient""s skin. Therefore, for preferred embodiments, the sensor is located within 5 mm of the second end of the waveguide, and for the most preferred embodiments the sensor is located within 1 mm of the second end.
Where a mechanism for removing heat is provided, such mechanism preferably includes a thermoelectric device having one side in thermal contact with the waveguide and an opposite side in thermal contact with a temperature sink. For a preferred embodiment of the invention, back-scattered radiation is substantially internally reflected within the optical waveguide, and there is a reflector within the waveguide for returning back-scattered radiation through the waveguide to the patient""s skin. While the reflector may be at a variety of locations within the waveguide, for a preferred embodiment, it is located at the first end of the waveguide. The reflector may also be along sides of the waveguide and the coefficient of reflection for areas of the reflector, either at the first end, the side walls or both, may be selected such that back scattered radiation which, before entering the waveguide, at angles nearer perpendicular to the patient""s skin are reflected more strongly than backscattered radiation which, before entering the waveguide, are at angles more nearly parallel to the skin surface. The second end of the waveguide in contact with the patient""s skin may also have an aperture which is at least substantially as great as the aperture of radiation back-scattered from the patient""s skin or a xe2x80x9creflection aperturexe2x80x9d substantially as great as the radiation back-scatter aperture may be achieved in other ways. For example, a reflector plate of size to provide the desired reflection aperture may surround the second end of the waveguide. More generally, the invention may include at least one waveguide passing through the head and terminating at a skin-contacting surface thereof, EM radiation being applied through the at least waveguide path to the patient""s skin; and a reflection means for returning back-scattered radiation to the patient""s skin, which reflection means has a reflection aperture at least substantially as great as the radiation back-scatter aperture. Reflection means may include at least a portion of the skin-contacting surface of the head, which portion may be in the form of a reflection plate, and may also include at least one reflection surface for back-scattered radiation entering the waveguide, at least part of which surface may be in the waveguide.
The system may be for treating a selected dermatological problem in a selected volume of a patient""s skin at a depth d which is below the DE junction. A source of EM radiation of a wavelength appropriate for treating the problem is provided along with an optical waveguide, a mechanism which cools the patient""s skin, at least in the portion thereof in contact with the waveguide when the second end of the waveguide is in contact with the patient""s skin, and a temperature sensor at the second end of the waveguide. The temperature at the sensor is indicative of the temperature at the patient""s DE junction. Finally, controls are provided which are operative in response to the sensor indicating that the DE junction has been cooled to at least a selected temperature for permitting radiation from the source to be passed through the waveguide to the patient""s skin. The cooling mechanism preferably removes heat from the waveguide; when in contact with the patient""s skin, the waveguide removing heat from and thus cooling the skin. The controls may also be operative in response to the sensor for maintaining the DE junction within a selected temperature range during application of radiation to the patient""s skin. The controls may also detect a selected temperature/time profile at the sensor, the profile being indicative of contact of the waveguide with the patient""s skin, and may prevent radiation from passing to the patient""s skin unless the predetermined profile is detected. This assures that radiation is not applied to the patient""s skin unless there is good thermal contact between the radiation-applying waveguide of the head and the patient""s skin. For preferred embodiments, the controls operate the cooling mechanism to cool the waveguide to a desired temperature, the controls being responsive to the sensor for determining when the desired temperature has been reached.
The controls may also be operative in response to the sensor sensing a selected increasing temperature profile at the sensor when the waveguide is placed in contact with the patient""s skin for permitting radiation from the source to be passed through the waveguide to the patient""s skin. This control may be instead of the control based on detection that the DE junction has been cooled to a selected temperature, but is preferably in addition thereto.
The enhanced retro-reflector features discussed above may also be used in the head independent of the temperature measuring features previously discussed, but are preferably used in conjunction therewith. The invention may also include a head having at least one optical waveguide for receiving EM radiation and for directing it to a skin-contacting surface of the at least one waveguide and a standoff having a first and a second end, with the first end surrounding the at least one waveguide at its lower end and forming a substantially air-tight seal therewith. The second end of the standoff is adapted to be in contact with the patient""s skin over the selected volume to form a chamber between the skin-contacting waveguide surface, the patient""s skin and walls of the standoff. A means is also provided for creating negative pressure in the chamber to draw the patient""s skin therein and into contact with the skin-contact surface. The walls of the standoff are preferable reflective to return back-scattered radiation to the patient""s skin. The means for creating negative pressure may include a hose mounted at one end to open into the chamber and connected at its other end to a source of negative pressure. Alternatively, the means for creating negative pressure may include the walls of the standoff being deformable when pressure is applied to the head/waveguide to permit the skin-contacting surface of the waveguide to contact the patient""s skin, forcing most of the air from the chamber, with the walls of the standoff returning to the their undeformed state when pressure is released, resulting in the creation of negative pressure in the chamber. For example, the walls of the standoff may be in the form of a bellows, suction cup or elastic ring.
Finally, rather than a single optical waveguide, the output surface of a first optical waveguide to which irradiation is initially applied may be mounted to a first surface of a second optical waveguide which also has a second skin-contacting surface opposite the first surface. Optical radiation received from the first waveguide is transmitted through the second waveguide to the skin-contacting surface thereof. The second skin-contacting surface of the second waveguide has a larger area than the output surface of the first waveguide and the second waveguide is formed to provide a larger optical aperture than of the first waveguide. The ratio of the spacing between the first and second surfaces of the second waveguide and a selected surface dimension of the skin-contacting surface of the second waveguide, for example the length of a side of the second surface or a diameter thereof, is approximately 1.5 to 1. Means may be provided for reflecting radiation back-scattered from the patient""s skin into the second waveguide back into the patient""s skin. The means for reflecting may include forming at least a portion of the first surface and/or other surfaces of the second waveguide so as to reflect radiation impinging thereon, and such reflection from the second waveguide may also be made angle dependent.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.